Geothermal energy is the energy naturally present inside the earth crust. When a large volume of hot water and steam is trapped in subsurface porous and permeable rock structure and a convective circulating current is set up, it forms a geothermal reservoir. A geothermal system can be defined as - convective water in the upper crust of earth, which transfers heat from a heat source (in the reservoir) to a heat sink, usually the free surface. A geothermal system is made up of three main elements: a heat source, a reservoir and a fluid, which is the carrier that transfers the heat. As an alternative source of energy geothermal energy has been under attention of the researchers for quite some time. The reason behind this is the existence of several benefits like clean and renewable source of energy which has considerable environmental advantage, with no chemical pollutants or wastes are generated due to geothermal emissions, and the reliability of the power resource. Hence research has been directed in several directions like exploration of geothermal resources, modeling the characteristics of different types of geothermal reservoirs and technologies to extract energy from them. The target of these models has been the prediction of the production of the hot water and steam and thus the estimation of the electricity generating potential of a geothermal reservoir in future years. In a geothermal power plant reinjection of the heat depleted water extracted from the geothermal reservoir has been a common practice for quite some time. This started for safe wastewater disposal and later on the technology was employed to obtain higher efficiency of heat and energy extraction. In most of the cases a very small fraction of the thermal energy present in the reservoir can be recovered without the reinjection of geothermal fluid. Also maintaining the reservoir pressure is essential which gradually reduces due to continuous extraction of reservoir fluid without reinjection, especially for reservoirs with low permeabilities. Although reinjection of cold-water has several benefits, the possibility of premature breakthrough of the cold-water front, from injection well zone to production well zone, reduces the efficiency of the reservoir operation drastically. Hence for maintaining the reservoir efficiency and longer life of the reservoir, the injectionproduction well scheme is to be properly designed and injection and extraction rates are to be properly fixed. Modeling of flow and heat transport in a geothermal reservoir due to reinjection of coldwater has been attempted by several researchers analytically, numerically and experimentally. The analytical models which exist in this field deal mostly with a single injection well model injecting cold-water into a confined homogeneous porous-fractured geothermal reservoir. Often the thermal conductivity is neglected in the analytical study considering it to be negligible which is not always so, as proved in this study. Moreover heterogeneity in the reservoir is also a major factor which has not been considered in any such analytical study. In the field of numerical modeling there also exists a need of a general coupled three-dimensional thermo-hydrogeological model including all the modes of heat transport (advection and conduction), the heat loss to the confining rocks, the regional groundwater flow and the geothermal gradient. No study existing so far reported such a numerical model including those mentioned above. The present study is concerned about modeling the non-isothermal flow and heat transport in a geothermal reservoir due to reinjection of heat depleted water into a geothermal reservoir. Analytical and numerical models are developed here for the transient temperature distributions and advancement of the thermal front in a geothermal reservoir which is generated due to the cold-water injection. First homogeneous geothermal aquifers are considered and later heterogeneities of different kinds are brought into picture. Threedimensional numerical models are developed using a software code DuMux which solves flow and heat transport problems in porous media and can handle both single and multiphase flows. The results derived by the numerical models have been validated using the results from the analytical models derived in this study. Chapter 1 of the thesis gives a brief introduction about different types of geothermal reservoirs, followed by discussion on the governing differential equations, the conceptual model of a geothermal reservoir system, the efficiency of geothermal reservoirs, the modeling and simulation concepts (models construction, boundary conditions, model calibration etc.). Some problems related with geothermal reservoirs and geothermal power is also discussed. The scenario of India in the context having a huge geothermal power potential is described and different potential geothermal sites have been pointed out. In Chapter 2, the concept of reinjection of the heat depleted (cold) water into the geothermal reservoir is introduced. Starting with a brief history of the geothermal reinjection, the chapter describes the purpose and the need of reinjection of geothermal fluid giving examples of different geothermal fields over the world where reinjection has been in practice and benefitted by that. The chapter further discusses on the problems and obstacles faced by the geothermal projects resulting from the geothermal reinjection, most important of which is the thermal-breakthrough and cooling of production wells. Lastly the problem of this thesis is discussed which is to model the transient temperature distribution and the movement of the cold-water thermal front generated due to the reinjection. The need of this modeling is elaborated which represents the motivation of taking up the problem of the thesis. Chapter 3 describes an analytical model developed for the transient temperature in a porous geothermal reservoir due to injection of cold-water. The reservoir is composed of a confined aquifer, sandwiched between rocks of different thermo-geological properties. The heat transport processes considered are advection, longitudinal conduction in the geothermal aquifer, and the conductive heat transfer to the underlying and overlying rocks of different geological properties. The one-dimensional heat transfer equation has been solved using the Laplace transform with the assumption of constant density and thermal properties of both rock and fluid. Two simple solutions are derived afterwards, first neglecting the longitudinal conductive heat transport and then heat transport to confining rocks. The analytical solutions represent the transient temperature distribution in the geothermal aquifer and the confining rocks and model the movement of the cold-water thermal front in them. The results show that the heat transport to the confining rocks plays an influential role in the transient heat transport here. The influence of some parameters, e.g. the volumetric injection rate, the longitudinal thermal conductivity and the porosity of the porous media, on the transient heat transport phenomenon is judged by observing the variation of the transient temperature distribution with different values of the parameters. The effects of injection rate and thermal conductivity have been found to be high on the results. Chapter 4 represents another analytical model for transient temperature distribution in a heterogeneous geothermal reservoir underlain and overlain by impermeable rocks due to injection of cold-water. The heterogeneity of the porous medium is expressed by the spatial variation of the flow velocity and the longitudinal effective thermal conductivity of the medium. Simpler solutions are also derived afterwards first neglecting the longitudinal conduction, then the heat loss to the confining rocks depending on the situation where the contribution of them to the transient heat transport phenomenon in the porous media is negligible. Solution for a homogeneous aquifer with constant values of the rock and fluid parameters is also derived with an aim to compare the results with that of the heterogeneous one. The effect of heat loss to the confining rocks in this case is also determined and the influence of some of the parameters involved, on the transient heat transport phenomenon is assessed by observing the variation of the results with different magnitudes of those parameters. Results show that the heterogeneity plays a major role in controlling the cold-water thermal front movement. The transient temperature distribution in the geothermal reservoir depends on the type of heterogeneity. The heat loss to the confining rocks of the geothermal aquifer also has influence on the heat transport phenomenon. In Chapter 5 another analytical model is derived for a heterogeneous reservoir where the heterogeneous geothermal aquifer considered is a confined aquifer consisted of homogeneous layers of finite length and overlain and underlain by impermeable rock media. All the different layers in the aquifer and the overlying and underlying rocks are of different thermo-hydrogeological properties. Results show that the advancement of the cold-water thermal front is highly influenced by the layered heterogeneity of the aquifer. As the cold-water thermal front encounters layers of different thermo-hydrogeological properties the movement of it changes accordingly. The analytical solution derived here has been compared with a numerical model developed by the multiphysics software code COMSOL which shows excellent agreement with each other. Lastly it is shown that approximation of the properties of a geothermal aquifer by taking mean of the properties of all the layers present will lead to erroneous estimation of the temperature distribution. Chapter 6 represents a coupled three-dimensional thermo-hydrogeological numerical model for transient temperature distribution in a confined porous geothermal aquifer due to cold-water injection. This 3D numerical model is developed for solving more practical problems which eliminate the assumptions taken into account in analytical models. The numerical modeling is performed using a software code DuMux as mentioned before. Besides modeling the three-dimensional transient temperature distribution in the model domain, the chapter investigates the regional groundwater flow has been found to be a very important parameter to consider. The movement of the thermal front accelerates or decelerates depending on the direction of the flow. Influence of a few parameters involved in the study on the transient heat transport phenomenon in the geothermal reservoir domain, namely the injection rate, the permeability of the confining rocks and the thermal conductivity of the geothermal aquifer is also evaluated in this chapter. The models have been validated using analytical solutions derived in this thesis. The results are in very good agreement with each other. In Chapter 7 the main conclusions drawn from the study have been enlisted and the scope of further research is also pointed out.

Geothermal research in the southern Canadian Cordillera has typically focused on hot spring systems and predicting maximum temperatures at depth, estimating fluid circulation depths, and investigating the distribution of hot spring systems and their relation to major geological features that often control thermal fluid flow. Detailed fieldwork to develop local and regional conceptual models of these systems has rarely been conducted and to our best knowledge, never in partnership with a First Nations. The scope of this project was to work collaboratively with the local First Nation to conduct detailed structural, hydrologic and hydrogeologic fieldwork to develop local and regional conceptual models of Sloquet Hot Springs, on unceded St'at'imc territory. To motivate our research and provide a successful example of geoscience research in the era of reconciliation and Indigenous resurgence, we review how resource regulation, research, reconciliation, and resurgence interact in British Columbia and detail our approach to community engagement. Detailed studies resulted in the development of a working conceptual model for the hydrogeothermal system at Sloquet Hot Springs. The conceptual model synthesizes local and regional groundwater flow, observed geothermal gradients, advective and conductive heat flow, as well as permeability contrasts in the subsurface to understand thermal fluid flow at the study site. Well monitoring, development, and pumping tests revealed numerous soft zones in the subsurface as well as bulk values for high transmissivity and hydraulic conductivity. Findings from subsurface investigations suggest bedrock in the area has significant permeability and that groundwater flow is controlled by steep hydraulic gradients caused by rugged topography in the region. The annual spring flux was calculated for Sloquet Hot Springs and used to approximate the recharge area that is required to drive the system. Although the study did not identify the primary fault that conveys high-temperature fluids, the potential locations of buried fault structures are hypothesized based on zones with observably high temperatures and flow along Sloquet Creek. / Graduate

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1980 / Vita. / Includes bibliographical references. / by Michael Benjamin Packer. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Mechanical Engineering

Shallow geothermal energy (SGE) systems are becoming increasingly popular due to both their environmental and economic value. By using the ground as a source and sink for thermal energy, SGE systems are able to more efficiently heat and cool structures. However, their utility beyond structural heating and cooling is being realized as their applications now extend to slab and pavement heating, grain and agricultural drying, and swimming pool temperature control. Relatively recently, SGE systems have been combined with deep foundations to create a dual purpose element that can provide both structural support as well as thermal energy exchange with the subsurface. These thermo-active foundations provide the benefits of SGE systems without the additional installation costs. One of the novel applications of thermo-active foundations is in bridge deck deicing. Bridge decks experience two main winter weather related problems. The first of which is preferential icing, where the bridge freezes before the adjacent roadway because the bridge undergoes hastened energy loss due to its exposed nature. The second problem is the accelerated deterioration of concrete bridge decks resulting from the application of salts and other chemicals that are used to prevent accumulation and/or melt the frozen precipitation on roads and bridges. By utilizing the foundation of a bridge as a mechanism by which to access the shallow geothermal energy of the subsurface, energy can be supplied to the deck during the winter to melt and/or prevent frozen precipitation. An experimental ground-source bridge deck deicing system was constructed and the performance is discussed. Numerical models simulating the bridge deck and subsurface system components were also created and validated using the results from the numerical tests. Furthermore, the observed loads that result in a foundation from bridge deck deicing tests are shown. In order to better design for these loads, tools were developed that can predict the temperature change in the subsurface and foundation components during operation. Mechanisms by which to improve the efficiency of these systems without increasing the size of the borehole field were explored. Ultimately this research shows that SGE can effectively be used for bridge deck deicing. / Ph. D.

This thesis studied the volcanic and geothermal source of arsenic (As) and its fate in shallow ground waters and upon entering the ocean by means of experimental and field measurements combined with geochemical modeling. Arsenic enters the atmosphere and hydrosphere from degassing magmas and during volcanic eruptions. The November 2004 eruption within the Vatnajökull Glacier, Iceland, provided an opportunity to study elemental fluxes from volcanic eruptions into the environment. According to geochemical modeling, lowering of pH due to magma gases during the eruption led to rapid tephra dissolution with corresponding change in flood water chemistry. Geochemical modeling of floodwater/seawater mixing indicated localised decrease in dissolved arsenic and sulphur due to adsorption on the suspended floodwater materials. As the floodwater was diluted the As desorbed and limited effect of the floodwater was predicted after thousand fold dilution. Laboratory experiments were carried out to generate and validate sorption coefficients for arsenite and arsenate in contact with basaltic glass at pH 3 to 10. The mobility of arsenite decreased with increasing pH. The opposite was true for arsenate, being nearly immobile at pH 3 to being highly mobile at pH 10. A 1D reactive transport model constrained by a long time series of field measurements of chemical composition of geothermal effluent fluids from a powerplant was constructed. Thioarsenic species were the dominant form of dissolved As in the waters exiting the power plant but converted to some extent to arsenite and arsenate before feeding into a basaltic lava field. Chloride, moved through the basaltic lava field (4100 m) in less than 10 yrs but arsenate was retarded considerably due to surface reactions and has entered a groundwater well 850 m down the flow path in accordance to prediction by the 1D model, which further predicted a complete breakthrough of arsenate in the year 2100 while arsenite will be retained for about 1000 yrs.

The East African Rift System is the world's major continental rift. While much geophysical and petrological attention has been paid to it, at least in the eastern branch ("Eastern Rift"), comparatively little research has been carried out into the geochemistry of rift fluids, despite the potential benefits to theoretical and practical studies. Hydrothermal activity provides the opportunity to sample a very wide range of waters and gases in the Eastern Rift. This thesis combines data from the literature with the results of the author's major investigation into Eastern Rift fluids carried out chiefly in Kenya, though with subsidiary investigations in Ethiopia and Djibouti. A synthetic approach has been adopted, whereby relationships and interactions are cross-referenced as far as possible to illuminate problems, thus demonstrating the usefulness of considering a wide range of fluids in the rift context. After reviews of physiography, geology, geothermics and hydrology of the Eastern Rift, the following topics are considered in detail: (i) chemical and isotopic evidence for water origin, movement and evolution, (ii) chemical and isotopic evidence for gas origin, movement and evolution, and (iii) fluid geothermometry. Within this context some specific aims have been pursued. The strong possibility of longdistance axial flows of groundwater has been shown by use of stable isotopic techniques. Further insights into alkaline hydrological discharge areas have been obtained by a combination of chemical and isotopic approaches. While carbon isotope ratios indicate an apparently homogeneous source of carbon dioxide, the existence of distinct mantle sources for volcanic rocks beneath different parts of the Eastern Rift has been comprehensively demonstrated by use of helium isotope ratios. Following the rather unsatisfactory performance of various gas geothermometers for evaluating geothermal system temperatures, a new relationship based on hydrocarbon breakdown has been developed. The possible use of oxygen isotopes in hydrothermal sinters as indicators of palaeoconditions has been investigated. In conclusion, topics worthy of further research in the Eastern Rift are suggested where the study of fluids would be of benefit.

The MH-2 science drill hole, on Mountain Home Air Force Base, Idaho, was drilled in 2012 to a total depth 1821 m as part of Project Hotspot. It encountered flowing artesian thermal water at 1,745 m below ground surface. This signature of a potential blind high temperature geothermal resource indicates that further analyses are needed to characterize the resource. Whole rock core was recovered to a total depth of 1821 m below ground surface and a suite of wireline logs collected. In this thesis I describe the lithologies represented in the core, correlate these lithologies to outcrop analogs, and identify and characterize petrophysical properties observable within the wireline logs, which represent fine-scale variations in stratigraphy, composition and/or alteration. The lithologies in the core are a series of basalts, brecciated and altered basalt, basaltic sands, carbonate-rich muds, and siliciclastic sediments. Basalt flows with evidence of increasing influence of an aqueous environment with time typify the lower half of core, whereas the upper half represents a period of diminished volcanism, lacustrine depositional environment, and a catastrophic water overflow event. The top of the core represents a resurgence of basaltic volcanism in the area. An overprint of brecciation at depth, fracturing, and secondary mineralization records the history of the geothermal system. All the elements of a relatively shallow and potentially energy generating geothermal resource are present at the MH-2 well location. These new data from the MH-2 borehole contributes to evaluating a parallel geothermal risk assessment of the Snake River Plain. Play fairway analysis was implemented for perhaps the first time in a geothermal regime. The Snake River Plain was divided up into three distinct play types; the area surrounding the Mountain Home Air Force Base was systematically identified as prospective. A region where sedimentary and altered rocks may create a seal, and blind faults create porosity in deep basalts.

Geothermal resources are characterized by a very low electrical resistivity of the reservoir formations. The application of electrical methods in the reconnaissance type exploration for such resources is discussed. It is concluded that the magneto-telluric method is very well suited for this purpose. In 1971 and 1972 a reconnaissance type magneto-telluric field program was carried out in southern and eastern Oregon by the Geophysics Group at Oregon State University. In order to reduce the field effort, the magnetic data were obtained from a fixed base station at Corvallis. Only the electrical field components were measured at the various field stations. Ten stations were occupied in the Klamath Falls area, six in central and eastern Oregon and one in the Willamette Valley. Impedance data were obtained in the .025 to 0.05 Hz frequency band of the Pc 3 micropulsations. The data were analysed on the basis of an individual event method. Only magnetic-telluric events with a good correlation are taken into account. The resulting apparent resistivities display some correlation with known geothermal manifestations in the region. The lowest resistivities of the order of 10 ohm-meters were recorded in the Klamath Falls region and at a station near Vale in eastern Oregon. As common in magneto-telluric work, the data display a considerable variability, irregular scattering and anisotropy. The results are encouraging in that they appear to indicate that the magneto-telluric method is a useful reconnaissance method in the regional exploration for geothermal resources. / Graduation date: 1974

Graduation date: 1979

Thesis (M.S.)--University of Nevada, Reno, 2008. / "December, 2008." Includes bibliographical references (leaves 82-85). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2009]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.